Systems that convert aircraft between cargo and passenger carrying capability must meet federally-mandated airworthiness requirements. Where passengers are concerned, these requirements have become especially stringent. Passenger seats must be able to retain their integrity with the aircraft structure under loads resulting from 16 g's of longitudinal deceleration--forces associated with a typical crash scenario.
It is also highly advantageous for such systems to be as light as practical. This is true for a variety of reasons.
From an economic point of view, additional structural weight subtracts directly from the maximum payload capability of an aircraft and increases fuel consumption. Heavier components also make the conversion process more difficult and time-consuming.
From a safety standpoint, even where maximum payload limits are not a factor, additional structural weight reduces an aircraft's thrust-to-weight ratio and increases wing-loading. Consequently, each additional pound of aircraft weight increases takeoff rolls and decreases refusal speeds thus limiting takeoff abort options and requiring longer runways. Increased wing loading also reduces airborne maneuverability, and reduces both accelerated and unaccelerated stall margins.
Unfortunately, current aircraft conversion systems lack the capability to withstand the forces that would result from 16 g's of longitudinal deceleration. In addition, current systems require heavy, structural, flight-critical passenger seat pallets. Current systems' seats are attached to a heavy structural pallet that can distribute the seat loads through its own structure. These pallets are locked into a previously-installed cargo conveyor system using pallet or container locks or special locks that are part of the cargo system. Multiple seat rows that are mounted on the pallets distribute all loads into the pallet and the pallet distributes the loads into the cargo system. The cargo system then distributes the load into the aircraft structure. Therefore, under current systems, pallets are load-bearing and flight critical.
For example, U.S. Pat. No. 3,381,921 to F. M. McDonough et al., issued May 7, 1968 and assigned to The Boeing Company, discloses passenger seats mounted to seat pallets. It also includes a cargo conveyor system comprising rail assemblies installed longitudinally in an aircraft floor and carrying conveying rollers for pallets. The '921 patent also discloses seat pallets having latches for gripping the rails of the cargo conveyor system and holding the seat pallets in their flight positions. Thus, with this design, the seats distribute all crash loads into the pallets which must distribute the loads through the cargo system and into the aircraft structure. The pallets must, therefore, be heavy load-bearing and flight-critical structures.